1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to the distribution of power to electronic circuits.
2. Description of the Relevant Art
With each new generation of computer systems, performance demands increase. One such demand relates to power distribution systems, which are required to supply increasing currents at lower voltages and lower impedances. These demands make design of a power distribution system increasingly difficult.
In many computer systems, processors and application specific integrated circuits (ASICs) are the chief consumers of power. Power is typically delivered to these components through a printed circuit board (PCB). Power distribution to a processor or ASIC can consume a significant portion of PCB resources, and is but one of several competing demands which must be considered during the PCB's design. Other demands include signal distribution and routing, component mounting, connector mounting, and so on. These demands are often times in conflict with one another, and thus compromises must be made to the design of the PCB. Such compromises may result in a less than optimal solution in addressing some or all of these demands.
Power distribution on a PCB typically involves at least one pair of copper planes (a power plane and a ground plane), along with a number of decoupling capacitors, typically mounted on a surface of the PCB. Since the PCB must also accommodate signal traces for a number of signals, the copper planes are often times perforated by holes known as vias. The presence of these signal vias may have a tendency to increase the inductance of the copper planes, which in turn results in an increase in impedance. Inductive impedance can be expressed by the formula Z=2πfL, wherein Z is the impedance, f is the frequency, and L is the inductance. Thus, the impedance of the power distribution system may be affected in large part by both the number of signal vias, as well as the frequency at which the computer system is designed to operate.
Further compounding problems of power distribution on a PCB is the fact that many computer systems required different voltages for various components. This may increase the number of copper planes needed for power distribution, as each voltage may require a separate power plane, and often times will have a separate ground plane as well. This may further increase the number of vias necessary in the PCB, thereby increasing the inductance of each of the power planes.